The surgery was the third operation on the 31-year-old's troublesome left shoulder, ABC said.

Thorpe, Australia's most decorated swimmer with 11 world championship golds, was admitted to hospital earlier this year to treat depression after he was found disoriented in Sydney.

Police were called when a resident saw Thorpe behaving oddly near a vehicle and his manager Erskine later said he had been taking a mixture of anti-depressants and medication for his shoulder.

Thorpe won three golds in his Olympic debut at the 2000 Sydney Games and clinched another two at Athens four years later, but surprised by announcing his retirement in 2006 at the age of 24, citing a lack of motivation.

Thorpe announced he would return to the pool in 2011 in a bid to qualify for the London Games but he flopped at national trials the following year and failed to make the team in either of his targeted 100 and 200 meters freestyle events.

Though describing the comeback as a fairytale "turned into a nightmare", Thorpe said he would continue swimming.

He later revealed in his 2012 autobiography "This is Me" of a near decade-long battle with depression, including suicidal thoughts and regular alcohol abuse.

Though frustrated by repeated injury problems, Thorpe last year told local media he had not ruled out a bid for the 2016 Games in Rio.